The neck measurement is 12" i'd like the cowl to be 14 -16" circumference so that it drapes a little after blocking.
With the scale down it seems like worsted weight yarn with size8 needles right off the bat is the right fit. Does this seem correct?

As for the rest, can anyone help me figure out the formula including short rows to scale down to the measurement and gauge I want?

Feels good to be back in the throw of things!!! Hope everyone's been well!

If you want to scale something down (or up for that matter), you will just need to cast on enough stitches to make it 14-16" in circumference. I don't know how many that will be because that depends on YOUR gauge. So you have to do a swatch... there goes that dirty word again! But once you know that, you can determine how many to cast on to make it any size YOU want with the yarn and needles YOU have. My cast on, of course, would be a little different because I don't knit at the same gauge you do.

As for the short rows, you will have to determine how much of a difference YOU want, and then calculate how many rows would be needed to achieve that. Again, depending on yarn and tension, your number of rows will be different than mine. Then you can determine how many extra rows are needed, and how you want to disperse them in the piece. This opens up a whole wide spectrum of design possibilities -- we each would produce something slightly different, and yet based on the same design -- and all would be correct, if we got what we wanted. That's the beauty of handknitting!!